This is a randomized, open-label, multi-center Phase III study evaluating the efficacy and safety of lapatinib in combination with trastuzumab versus trastuzumab alone as continued HER2 suppression therapy in women with HER2-positive metastatic breast cancer (MBC). Eligible subjects will have completed 12 to 24 weeks of first- or second-line treatment with trastuzumab plus chemotherapy, experienced either complete disappearance of all metastatic lesions, or persistence of metastatic disease (stable disease) without unequivocal progression or the occurrence of new lesions, and been indicated to continue to receive trastuzumab alone as maintenance therapy. Eligible subjects entering the LPT112515 study on first-line treatment will have no known history of central nervous system (CNS) metastases; subjects entering the study on second-line treatment will have no known history of CNS metastases or have stable (asymptomatic and off steroids ≥3 months) CNS metastases. The primary objective of this study is to compare progression-free survival (PFS) in subjects with HER2-positive MBC randomized to receive treatment with lapatinib plus trastuzumab versus those randomized to receive trastuzumab alone. The secondary objectives include overall survival, clinical benefit response rate (CR, PR or SD ≥24 weeks) and the qualitative and quantitative adverse event profile of the 2 treatment arms. It is estimated that 280 subjects (140 per group) will be required to observe 193 PFS events.

Concurrent disease or condition that may interfere with study participation, or any serious medical disorder that would interfere with the subject's safety (for example, active or uncontrolled infection or any psychiatric condition prohibiting understanding or rendering of informed consent)

Women of childbearing potential, including women whose last menstrual period was <12 months ago (unless surgically sterile) who are unable or unwilling to use adequate contraceptive measures during the study treatment period. Adequate contraception includes intra-uterine device, barrier methods with spermicide, or oral contraceptives (unless clinically contraindicated for the subject population or per local practice, refer to protocol for further details)

Pregnant or lactating females

Any clinically significant gastrointestinal abnormalities that may alter absorption such as malabsorption syndrome or major resection of the stomach or bowels.

Known immediate or delayed hypersensitivity reaction or idiosyncrasy to drugs chemically related to any of the study agents or their excipients that, in the opinion of the Investigator or GSK medical monitor , contra-indicates participation

Contacts and Locations

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Please refer to this study by its ClinicalTrials.gov identifier: NCT00968968